1. Field of the Invention
The present invention relates to an electric razor and more particularly to an electric razor that includes an inner rotary cutter which can reduce the load and frictional resistance relative to the power source and outer cutter.
2. Prior Art
In rotary electric razors, the inner cutters are rotated under the outer cutters, and the whiskers are cut by the shearing force provided by the outer and inner cutters. There is an electric razor having a single shaving unit that consists of a single inner cutter and a single outer cutter installed in a head frame of a razor. There is also another type of electric razor that has three shaving units arranged in an equilateral triangle shape on a head frame.
FIG. 8 illustrates the relationship between the outer cutter and the inner cutter. The explanation of the cutters will be made below referring to how the whiskers are cut by the cutters.
More specifically, the outer cutter 2 has openings or slits 2a on the top surface. Whiskers penetrate the slits 2a into the razor and are cut by the sliding action of cutter blades 4a (only one shown in this Figure) of the inner cutter 4 which is in contact with the outer cutter 2 and rotates in the direction of the arrow. In other words, the whiskers are cut by the outer cutter 2 and the rotating inner cutter 4. The cutter blades 4a of the inner cutter 4 are inclined in the rotational direction of the inner cutter.
There are different types of inner cutters. One of them is an inner cutter obtained by cutting and bending a plurality of projections from the circumferential edge portion of a cutter disk that is made out of metal or other materials.
When shaving is done, grease secreted out of the skin is mixed with shaving debris of the sheared whiskers. As a result, the shaving debris easily adheres to the surfaces of the cutter blade, particularly to the rear side surface 4b of the cutter blade 4a that faces the opposite direction from the direction of the rotation of the inner cutter. More specifically, if the shaving debris 5 and other substances adhere to the cutter blades, the frictional resistance between the inner cutter and outer cutter increases. This means that the load applied on the driving source (or motor) increases, resulting in high power consumption. Moreover, the rotational speed of the inner cutter goes down and the cutting or shaving performance drops. Thus, cleaning of the inner cutter 4 is inevitable.
Furthermore, when the frictional resistance between the inner and outer cutters is increased, heat is generated, which imparts an unpleasant sensation to the skin. In addition, the generation of heat accelerates wear in the inner and outer cutters and may damage them eventually.
In a conventional electric razor, a spring is used so that the cutter blades, or its tip ends, of the inner cutter are urged so as to keep contact with the inner or bottom surface of the outer cutter. In this structure, if the area of contact between the outer and inner cutters is large, a large load is proportionally applied on the inner cutter, and this causes the increase of power consumption.
In the inner cutter which has cutter blades integral with a metal cutter disk, the cutter blades are obtained, as described above, by cutting and bending the circumferential edge portion of a round metal disk. Thus, the thickness of the cutter disk will be the thickness of the cutter blade, which is referred to by A in FIG. 8. As a result, it is necessary that a cutter disk be as thin as possible so as to obtain thin cutter blades in order to keep the friction between the inner and outer cutters as small as possible. When, however, the cutter disk as a whole is thin, the overall strength of the cutter blades is impaired. In other words, in conventional inner cutters, the reduction in the thickness of the cutter blade and the assurance of the overall strength of the cutter blades is in conflict and has been unsolved.